Many attempts have been made to answer the question of whether tyrannosaurs were active predators -- seeking out and killing their prey or were scavengers, waiting for the opportune moment to step in and satisfy their hunger. Joining this debate, researcher William Abler and his colleagues have literally looked inside this amazing dinosaur's mouth for clues and come up with some surprising results.

The enormous teeth of the tyrannosaur would seem like the perfect killing tool with sharp points and serrations on both the front and back edges. But when put to an actual test of bone crushing and flesh tearing, would they live up to this perfect image?

Abler and his associates wondered about the serrations seen on the teeth, and whether they would serve the same purpose as those on common kitchen knives. Since no studies had been done regarding knife edges, Abler set up an experiment with serrated blades and tyrannosaur tooth edges.

By creating a series of standardized knife edges, including a serrated edge, the scientists were able to study cuts or tears on actual pieces of meat and simulate biting experiences similar to those that might have been demonstrated by the dinosaur.

The blades were "mounted on a butcher's saw operated by cords and pulleys" that created a sawing action on several same-sized pieces of meat. While the straight edge split the meat, a serrated knife edge "gripped and ripped" it.

A serrated fossil tooth of the ancient shark Carcharodon megalodon produced similar results. When a tyrannosaur tooth was placed in the mechanism, it produced cuts similar to those made by a smooth knife blade that was in need of sharpening. Questioning these results, Abler wondered: if the menacing tooth edges were not sharp, what were they for?

When comparing the serrations of the tyrannosaur tooth with those of the ancient shark, Abler saw major differences in the shape of the points and in the spaces between the points, or cella. The shark's tooth had pyramidal-shaped points. while those of tyrannosaurs were cube-like.

Putting the teeth of Albertosaurus to the meat test, the scientists discovered food particles and grease trapped in the cella. According to Abler, when such particles remain in the mouth they become the sites for septic bacteria which can result in fatal bites to victims.
This indicated that tyrannosaurs might have been able to merely bite their victims and sit back and wait for them to succumb to the fatal infection.

A "puncture and pull" method of biting seemed most apparent to Abler, where the dinosaur's teeth acted as pegs that more or less held the victim. Also, due to the non-articulating surface of the teeth, he hypothesized that tyrannosaurs did not chew their food but swallowed it whole.

Abler cites a study of the Indonesian Komodo dragon (Varanus komodoensis), whose teeth are similar in shape to those of tyrannosaurs. Ciofi's study has led the paleontologist James O. Farlow to suggest a positive comparison between the two animals. Since the Komodo dragon sometimes hunts by biting its prey and then waiting for it to die through an infection of the wound, why wouldn't this be possible in tyrannosaurs?

[People bitten by a Komodo dragon more frequently die from sepsis than from the damage inflicted by the wound itself. -- Ed]

Abler adds that with tightly closed lips, tyrannosaur teeth may have pierced their own gums, which would then have bled and nourished the septic dental bacteria. This would have provided perfect conditions for poisoning future prey.

With an interest in form and movement of the vertebrate animal -- and particularly how these are expressed in the T. rex -- paleontologist Gregory Erickson delves deeply into the predator/scavenger theories associated with this animal, taking a somewhat different tack than Abler, whose study is also presented in the same issue of Scientific American.

Not being one who is satisfied with the idea that function follows form, Erickson includes himself in the "new breed of scientists" known as paleobiologists (Just as the Samasaurus rex is a "paleoethnoherpetologist) . These scientists take the seemingly hard route in searching for explanations for movement not related exclusively to the animal's anatomy.

For this new breed of scientist, clues can be found in sites where groups of dinosaur fossils are found together, in bite marks on bones, and surprisingly -- in coprolites (dino dung)! Using data from the early Tyrannosaurus along with others with similar life styles, such as Albertosaurus, Gorgosaurus and Daspletosaurus, greatly helps the investigation.

When small congregations of T. rex were found together in a site, as was the case in the Hell Creek Formation in eastern Montana, scientists wondered about possible group dynamics of these creatures. Then when a group of albertosaur specimens, presumed comparable to tyrannosaurs in social behavior, were recently rediscovered, they knew they would have a chance to do a more in-depth study.

Paleontologist Philip J. Currie and other scientists from the Royal Tyrrell Museum of Palaeontology dove into the examination and came up with some exciting results. Their conclusions refuted the scavenging theory when they found no evidence that the animals had congregated to take advantage of a mud-hole-stranded, or otherwise trapped, herbivore.

Instead, Currie hypothesized, the albertosaurs were most likely a family group that had been killed in some sort of natural disaster. This kind of information has helped to lay the groundwork for determining social behavior of tyrannosaurs as well.

Another study by Currie and Tanke discusses bite marks made by fighting between theropods, including T. rex. The dinosaurs would have bitten each other, with heads at the same level, using the sides of their mouths rather than attacking from the front.

Bite marks discovered on a pelvis of an adult Triceratops identified by Erickson in 1992 became the "first definitive bite marks from a T. rex". Erickson describes the dinosaurs' method of eating as the "puncture and pull" technique, as does Abler, but does not think food was swallowed whole.

In testimony to this he cites a recently discovered 44 cm long coprolite, presumed to be from a T. rex, containing a large amount of chewed and digested bone.

This same behavior is seen in T. rex's relationship with a common herbivore of the Cretaceous. T. rex bite marks found in an Edmontosaurus bone bed testify to the theropod's scavenging behavior, while its predaceous bite marks can also be found on the healed-over tail vertebrae of an Edmontosaurus that escaped attack. The debate continues.